1. Field of the Invention
The invention pertains to compositions comprising inorganic oxide-supported organometallic compounds of Groups II, III and IV of the Periodic Table, their preparation and their use in the purification of fluids, such as hydrocarbons and particularly the purification of solvents and olefins.
2. Related Art
Billions of pounds of ethylene, propylene and 1-butene are polymerized each year in the United States. The primary products are low-density polyethylene (LDPE), linear low-density polyethylene, high-density polyethylene and polypropylene. While the production processes vary widely, all polymerization processes use sophisticated catalyst systems that are vulnerable to poisoning by various impurities. Polyolefin producers, therefore, usually employ elaborate and expensive processes to remove the undesirable impurities, not only from the olefin monomers but also from the process solvents and nitrogen gas used for blanketing the system.
There is a strong trend toward the use of advanced catalysts which produce so much polymer per pound of catalyst that the producer does not have to de-ash the crude polymer to remove any catalyst residue. Such a change affords a substantial increase in yield and a simultaneous reduction in operating costs. It also reduces the capital cost of a new plant significantly. These new super-active catalysts are much more susceptible to poisoning than their predecessors.
The major catalyst poisons are reactive impurities (e.g., CO.sub.2, CO, COS, H.sub.2 O, H.sub.2 S, O.sub.2, and acetylenics) in the olefin monomers. Although extensive purification is being done in most plants, current technology is usually not adequate to achieve the more stringent purity specifications necessary to realize the full benefits of the advanced catalysts. As the quantity of polymer produced from each pound of catalysts is increased, e.g., five- to ten-fold, the amount of feedstock impurities that can be tolerated decreases correspondingly. Total reactive impurities may have to be reduced to one hundred parts per billion or less. Further, current purification processes do not always afford adequate protection against upsets caused by "spikes" of impurities in the monomer, regardless of the purification system being used.
It is known in the prior art to purify olefins by various processes usually entailing treating the olefin with absorbents such as silica gel or ignited aluminum oxide, diethyl zinc, or with a solution containing triethyl aluminum, tripropyl aluminum, triisobutyl aluminum, trimethyl aluminum, triphenyl aluminum, etc.
U.S. Pat. No. 3,202,645 discloses a surface treated inorganic, solid polymerization catalyst wherein the catalyst comprises a reaction product of a compound of a metal chosen from Groups IIb to IIIb of the Periodic Table the hydroxyl groups on the surface of a finely divided particulate inorganic solid and a halide-type compound of Groups IVa, V, VIa, VIIa or period 4 of a Group VIII metal. The finely divided particulate material of the reference is said to be less than about 1 micron and preferably less than about 0.1 micron. The reference, therefore, is directed to the use of extremely fine powders. The reaction product of the reference is then combined with a transition metal halide for use in polymerization processes.
U.S. Pat. No. 3,274,120 discloses a catalyst composition having increased hydroxyl groups bound thereto and the method of producing the composition. The composition and method taught comprises the use of a finely divided solid support material. The particle size of the support disclosed describes a fine powdery material.
U.S. Pat. No. 3,620,981 discloses a heterogenous catalyst composition comprising a hydrocarbon complex of certain transition metal halides supported on an acidic inorganic oxide catalyst support, which support is optionally pretreated with an alkyl aluminum compound prior to incorporation of the transition metal halide. The alkyl aluminum compounds generically (and apparanently incorrectly) represented by R".sub.y AlX.sub.(31y), where R" is an alkyl of up to 8 carbon atoms; X is a halogen and y is a whole number from one to three. Compounds listed include triethyl and triisobutyl aluminum. From the examples provided it can be concluded that the inorganic oxide support material is a powder.
An article appearing in the Journal of Catalysis, Vol. 7, pages 342 to 351 (1967) entitled "Hydroxyl Groups on Silica, Alumina, and Silica-Alumina Catalysts" by Sato et al. describes experimental methods used to characterize the surface hydroxyls on silica, alumina, and silica-alumina solids. In the experiments therein, which were carried out in a closed system under normal nitrogen atmosphere, the volume of alkane produced from the reaction of a metal alkyl with the surface hydroxyls was measured. In the experiments, the alumina was prepared by hydrolysis of redistilled aluminum isopropoxide in isopropyl alcohol with distilled water, was washed, filtered, dried at 120.degree. C. and then calcined at 500.degree. C. for 2 hours (see page 343). The procedure as described on page 344 comprised calcining about 0.2 gram of a catalyst at 450.degree. C. in a reactor which is slowly heated under a nitrogen atmosphere then evacuated to 10.sup.-2 to 10.sup.-3 mm Hg for 2 hours, then cooled to room temperature and brought back to atmospheric pressure with nitrogen. Then 1.0 to 1.5 mls of the organometallic compound, e.g., triethyl aluminum, which comprised about four or five equivalents of the organometallic compound to the one of surface hydroxyl groups, was poured into the reactor and the volume of the evolved gas was measured to determine the number of surface hydroxyl groups. It is apparent from the above description that the alumina utilized in the system was powdered alumina since there is no indication that the alumina produced by the process disclosed above was shaped. The solvent utilized in the process was decalin which is a very high boiling point solvent not suitable for use in a commercial process of purifying hydrocarbons since the decalin would remain in the system and be carried over during the purification process. Further, the process described in Sato utilizes a four to five fold excess of triethyl aluminum to hydroxyl groups whereas the instant process uses about a two fold excess of organometallic to metal oxide. As a result of the above, the material which would have been prepared by the process disclosed by Sato would not be useful as a purification media for liquids or gaseous feed streams.
A paper entitled "Lanthanide Catalysts for the Polymerization of Olefins" by Ballard et al. appearing in European Plastics and Rubbers Conference, 5th, Paris, 1978, part A-4, pages 1-7, briefly discloses on page 3 thereof, line 2, "ethylene gas (purified by BTS catalyst, molecular sieve and AlEt.sub.3 /Al.sub.2 O.sub.3) . . . ". The paper utterly fails to elucidate what is meant by the ambiguous abbreviation "AlEt.sub.3 /Al.sub.2 O.sub.3 ". The indication is that ethylene gas is purified by this system. There is no further disclosure relative to the purification of ethylene or any other olefin and more importantly, there is no reference, teaching or suggestion for purifying liquid feed streams.
French Pat. No. 1,462,762 describes the purification of propylene with a liquid aluminum alkyl. Gaseous propylene in the process is purified by a countercurrent system of liquid tripropyl aluminum. Countercurrent contact with a liquid aluminum alkyl is not a commercially useful process, however, because there will be significant entrainment of aluminum alkyl in the gas stream. This could cause deleterious effects downstream.
None of the cited art disclosed a purifying agent comprised of a granular metal oxide-supported organometallic compound prepared by either utilizing a granular inorganic oxide starting material or by utilizing a powder which is shaped after preparation.